316 research outputs found
Control oriented modelling of an integrated attitude and vibration suppression architecture for large space structures
This thesis is divided into two parts. The main focus of the research, namely active vibration control for large flexible spacecraft, is exposed in Part I and, in parallel, the topic of machine learning techniques for modern space applications is described in Part II. In particular, this thesis aims at proposing an end-to-end general architecture for an integrated attitude-vibration control system, starting from the design of structural models to the synthesis of the control laws. To this purpose, large space structures based on realistic missions are investigated as study cases, in accordance with the tendency of increasing the size of the scientific instruments to improve their sensitivity, being the drawback an increase of its overall flexibility. An active control method is therefore investigated to guarantee satisfactory pointing and maximum deformation by avoiding classical stiffening methods. Therefore, the instrument is designed to be supported by an active deployable frame hosting an optimal minimum set of collocated smart actuators and sensors. Different spatial configurations for the placement of the distributed network of active devices are investigated, both at closed-loop and open-loop levels. Concerning closed-loop techniques, a method to optimally place the poles of the system via a Direct Velocity Feedback (DVF) controller is proposed to identify simultaneously the location and number of active devices for vibration control with an in-cascade optimization technique. Then, two general and computationally efficient open-loop placement techniques, namely Gramian and Modal Strain Energy (MSE)-based methods, are adopted as opposed to heuristic algorithms, which imply high computational costs and are generally not suitable for high-dimensional systems, to propose a placement architecture for generically shaped tridimensional space structures. Then, an integrated robust control architecture for the spacecraft is presented as composed of both an attitude control scheme and a vibration control system. To conclude the study, attitude manoeuvres are performed to excite main flexible modes and prove the efficacy of both attitude and vibration control architectures. Moreover, Part II is dedicated to address the problem of improving autonomy and self-awareness of modern spacecraft, by using machine-learning based techniques to carry out Failure Identification for large space structures and improving the pointing performance of spacecraft (both flexible satellite with sloshing models and small rigid platforms) when performing repetitive Earth Observation manoeuvres
Mastering Uncertainty in Mechanical Engineering
This open access book reports on innovative methods, technologies and strategies for mastering uncertainty in technical systems. Despite the fact that current research on uncertainty is mainly focusing on uncertainty quantification and analysis, this book gives emphasis to innovative ways to master uncertainty in engineering design, production and product usage alike. It gathers authoritative contributions by more than 30 scientists reporting on years of research in the areas of engineering, applied mathematics and law, thus offering a timely, comprehensive and multidisciplinary account of theories and methods for quantifying data, model and structural uncertainty, and of fundamental strategies for mastering uncertainty. It covers key concepts such as robustness, flexibility and resilience in detail. All the described methods, technologies and strategies have been validated with the help of three technical systems, i.e. the Modular Active Spring-Damper System, the Active Air Spring and the 3D Servo Press, which have been in turn developed and tested during more than ten years of cooperative research. Overall, this book offers a timely, practice-oriented reference guide to graduate students, researchers and professionals dealing with uncertainty in the broad field of mechanical engineering
Development of Magnetic Shape Memory Alloy Actuators for a Swashplateless Helicopter Rotor
Actuator concepts utilizing NiMnGa, ferromagnetic shape memory alloy are investigated for potential use on a smart rotor for trailing edge flap actuation. With their high energy density, large dynamic stroke, and wide operating bandwidth, ferromagnetic shape memory alloys (FSMA) like NiMnGa, seem like attractive candidates for smart rotor actuators, potentially able to fulfill the requirements for both primary rotor control and vibration suppression. However, because of the recent discovery of the material, current experimental data and analytical tools are limited.
To rectify these shortcomings, an extensive set of detailed experiments were conducted on samples of NiMnGa to characterize the response of the alloy for a wide variety of mechanical and magnetic loading conditions. Measurements of the material performance parameters such as power density, damping properties, magneto-mechanical coupling, and transduction efficiency were included. Once characterized, the experimental data were used to develop a series of analytical tools to predict the behavior of the material. A model, developed in parallel to thermal shape memory alloy models is proposed to predict the quasi-static stress-strain behavior. A simple, low frequency, parameter based model was also developed to predict the alloy's dynamic strain response.
A method for developing conceptual actuators utilizing NiMnGa as the actuation element was proposed. This approach incorporates experimental data into a process that down-selects a series of possible actuator configurations to obtain a single configuration optimized for volumetric and weight considerations. The proposed actuator was designed to deliver 2 mm of stroke and 60 N of force at an actuation frequency of 50 Hz. However, to generate the 1.0 T magnetic field, the actuator mass was determined to be 2.8 kg and required a minimum of 320 Watts of power for operation. The mass of the NiMnGa element was only 18.3 g.
It was concluded that although the NiMnGa alloy was capable of meeting the trailing edge flap actuation requirements, the material is not suitable in its present form for this application because of weight and power consumption issues. The magnetic field requirements must be reduced to improve the utility of the material for rotorcraft applications
Micro-manufacturing : research, technology outcomes and development issues
Besides continuing effort in developing MEMS-based manufacturing techniques, latest effort in Micro-manufacturing is also in Non-MEMS-based manufacturing. Research and technological development (RTD) in this field is encouraged by the increased demand on micro-components as well as promised development in the scaling down of the traditional macro-manufacturing processes for micro-length-scale manufacturing. This paper highlights some EU funded research activities in micro/nano-manufacturing, and gives examples of the latest development in micro-manufacturing methods/techniques, process chains, hybrid-processes, manufacturing equipment and supporting technologies/device, etc., which is followed by a summary of the achievements of the EU MASMICRO project. Finally, concluding remarks are given, which raise several issues concerning further development in micro-manufacturing
Control Strategies for Piezoelectrically Actuated Fast Mechanical Disconnect Switches for Hybrid Circuit Breakers
Piezoelectrically-actuated fast mechanical switches provide a low-loss conduction path in hybrid circuit breakers for medium-voltage, direct-current system protection. With the desired actuation performance being pushed towards the driving limit of the piezoelectric actuator, excessive vibration starts to dominate the underdamped travel curves of contact movements, which will lead to insulation failures and delayed operations in the fast mechanical switch. To improve underdamped responses into critically damped actuations, several switching motion control strategies have been proposed with active damping filters such as notch, lead and lag compensators in the closed-loop system. The switching motion controllers are built upon a vibrational dynamics model of a prestressed piezoelectric stack actuator with experimentally identified parameters. The controller tuning principles are derived to achieve optimized step responses with a minimized rising time down to 250 ÎŒs, a reduced undershoot around 10%, and a closed-loop control bandwidth up to 1760 Hz. The closed-loop simulation is performed to verify the performance of proposed switching motion controllers on both low-frequency external disturbance elimination and high-frequency internal vibration attenuation. According to the hardware implementation tests, the proposed control strategies have optimized the switching motions of a heavily loaded piezoelectric actuator with a 60% reduction in undershoot and a 45% reduction in settling time. At the same time, the sub-millisecond switching time has been preserved in the actively damped travel curves of this piezoelectric actuator. With optimized switching operations of the piezoelectric actuator, the overall fast mechanical switch can better serve the advanced hybrid circuit breakers to achieve reduced fault current and fault clearance time during circuit interruptions. Consequently, the overall medium-voltage direct-current systems can get better protected by the piezoelectrically-actuated fast mechanical switch.Ph.D
Vibration Energy Harvesting for Wireless Sensors
Kinetic energy harvesters are a viable means of supplying low-power autonomous electronic systems for the remote sensing of operations. In this Special Issue, through twelve diverse contributions, some of the contemporary challenges, solutions and insights around the outlined issues are captured describing a variety of energy harvesting sources, as well as the need to create numerical and experimental evidence based around them. The breadth and interdisciplinarity of the sector are clearly observed, providing the basis for the development of new sensors, methods of measurement, and importantly, for their potential applications in a wide range of technical sectors
Performance of Active Vibration Isolation in the Advanced LIGO Detectors
The second generation of LIGO detectors has finished construction and the commissioning effort is pushing the instruments towards their designed sensitivity. Around the world similar undertakings are underway, and soon a global network capable of astrophysical observation will be operational. The first sentences are being written in an important chapter of terrestrial gravitational wave detection, an entire century after the theoretical foundations of general relativity were laid, and after decades of calculation, design, proposals, plans, and laboratory work. In order to make sensitive measurements, the detector must be well isolated from the vibrations of the ground, and much of this thesis describes the effectiveness of active control platforms used to mitigate the transmission of seismic motions to the test masses. This work was performed both during the last science run of the first generation LIGO detector and as part of the commissioning of the second generation instrument
Technology for large space systems: A bibliography with indexes (supplement 17)
This bibliography lists 512 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1, 1987 and June 30, 1987. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems
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4D printing of soft orthoses for tremor suppression
Tremor is an involuntary and oscillatory movement disorder that makes daily activities difficult for affected patients. Hand tremor-suppression orthoses are noninvasive, wearable devices designed to mitigate tremors. Various studies have shown that these devices are effective, economical, and safe; however, they have drawbacks such as large weight, awkward shape, and rigid parts. This study investigates different types of tremor-suppression orthoses and discusses their efficiency, mechanism, benefits, and disadvantages. First, various orthoses (with passive, semi-active, and active mechanisms) are described in detail. Next, we look at how additive manufacturing (AM) has progressed recently in making sensors and actuators for application in tremor orthoses. Then, the materials used in AM are further analyzed. It is found that traditional manufacturing problems can be solved with the help of AM techniques, like making orthoses that are affordable, lighter, and more customizable. Another concept being discussed is using smart materials and AM methods, such as four-dimensional (4D) printing, to make orthoses that are more comfortable and efficient
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